1. Field of the Invention
The invention relates to particle-optical components for manipulating a plurality of beamlets and particle-optical arrangements and electron-beam inspection systems comprising such particle-optical components. Further, the invention relates to a method of manipulating charged particle beamlets, a method of focusing a plurality of charged particle beamlets and methods for manufacturing multi-aperture plates suitable for use in the particle-optical components. In addition, the invention pertains to a charged-particle multi-beamlet lithography system and a method of writing a pattern on a substrate.
The invention may be applied to charged particles of any type, such as electrons, positrons, muons, ions (charged atoms or molecules) and others.
2. Brief Description of Related Art
The increasing demand for ever smaller and more complex microstructured devices and the continuing demand for an increase of a throughput in the manufacturing and inspection processes thereof have been an incentive for the development of electron microscopy systems that use a plurality of primary electron beamlets in place of a single electron beam, thus significantly improving the throughput of such systems. However, the use of multiple beamlets brings about a whole range of new challenges to the design of electron-optical components, arrangements and inspection and processing systems such as microscopes and lithography systems. A particle-optical arrangement for forming a plurality of charged-particle beamlets wherein the beamlets are arranged in an array pattern is described in WO 2005/024881 A2 (U.S. provisional application Ser. No. 60/500,256) to the same Assignee.
In general, such particle-optical arrangements and inspection and lithography systems comprising same use a plurality of charged particle beamlets focused on a specimen to be inspected. In case of an embodiment of an inspection system using electrons as charged particles, for example, an electron source provides a single beam of primary electrons (or, alternatively, multiple beamlets from an array of particle sources), which is incident on a multi-aperture plate having a plurality of apertures formed therein for generating a plurality of beamlets from those electrons of the single beam of electrons that pass through the apertures of the multi-aperture plate. The plurality of electron beamlets is focused on the substrate generally by means of a focussing particle-optical lens downstream of the multi-aperture plate. An array of primary electron spots is thus formed on the substrate. Secondary electrons emitted as a result of impinging primary electrons follow a secondary electron beam path to a respective one of a plurality of detector pixels of a CCD electron detector, with a beam path of beamlets of the primary electrons and the beam path of the beamlets of secondary electrons being separated by means of beam separator, such as a Wien-type filter. This arrangement allows to use a single electron-optical column. Such a system is described in detail in WO 2005/024881 A2 to the same Assignee, as mentioned before.
Using such an array or pattern of beamlets of primary electrons requires the electron optical system to provide those beamlets in a reliable and accurate manner such that the beamlets show little, if any, variation in intensity, deviation from a predetermined position within the array, variation in optical properties, such as aberrations and the like. The quality of the array of beamlets and, correspondingly, the quality of the array of primary electron spots generated in an image plane will be dependent on both the properties of the multi-aperture plate used and the characteristics of other components or elements in the electron-optical arrangement. Components upstream of the multi-aperture plates will influence, amongst others, a quality of the single electron beam which will also have an impact on the beamlets generated therefrom. Components downstream of the multi-aperture plate will, amongst others, influence on how well the array of beamlets may be transferred onto the specimen to form primary electron spots. What has been described above for systems using electrons as charged particles is equally applicable to other kinds of charged particles.
Given the requirement to provide a precisely defined array of beamlets of charged particles in order to achieve a satisfactory performance of the entire system, there is a constant need to improve on a performance of such a particle-optical system.
In U.S. provisional application US 60/500,256 to the same Assignee as cited above, multi-aperture plates of different configurations are disclosed. In one aspect, multi-aperture plates having apertures that vary in size or shape depending on their position on the plate or having the apertures displaced from a respective position in a strictly regular pattern are disclosed. Those changes to aperture size/shape and position allow to correct imaging errors such as a distortion. In addition, a multi-aperture plate having a resistor-network disposed thereon is described, the resistor network being configured such that a voltage applied to the multi-aperture plate results in groups of apertures having a different potential. Since the potential applied to an aperture is related to a focusing effect provided by said aperture, the apertures can be configured to have different focussing effects such that a field curvature of the particle-optical system can be corrected.
Although good results can be achieved with the above-described multi-aperture plates, the above described approaches to correct imaging errors of the particle-optical system require multi-aperture plates having apertures that vary in at least one of shape and size and pattern, or having a resistor network, which is often associated with an increase of a complexity of the manufacturing process. In addition, the capacity for correction of imaging errors can typically not be dynamically adjusted in any suitable manner when an imaging error of a particle-optical system changes or the component would need transferring to a different system having different properties. For example, a field curvature introduced by the imaging optics may dynamically change with a change of a total beam current transmitted by the optical system due to space charge effects.
It is therefore an object of the present invention to provide particle-optical components and arrangements for manipulating beams and beamlets of charged particles that enhance an overall performance of a particle-optical system comprising said particle-optical component/arrangement.
It is a further object of the present invention to provide particle-optical components and arrangements for manipulating beams or beamlets that are configured to correct at least one imaging error of a system comprising said particle-optical component/arrangement. Preferably, the one or more imaging errors comprise in particular one or more aberrations, that are field-dependent, i.e. dependent on a position within a respective field. Examples of imaging errors are a field curvature and any other geometrical aberration, such as coma.
It is another object of the present invention to provide a particle-optical component and arrangement that is configured to correct an imaging error of the particle-optical system it is comprised in with a higher degree of flexibility.
It is also an object of the present invention to provide a particle-optical component and arrangement configured to correct an imaging error of the particle-optical system it is comprised in, wherein the extent of the correction provided may be adjusted.
It is an additional object of the present invention to provide charged particle inspection and lithography systems comprising particle-optical components and arrangements that meet any of the above objects. It is also an object to provide an improved method of writing a pattern on a substrate.
It is a further object of the present invention to provide a particle-optical component capable of providing a correction for a particle-optical aberration that is suitable for use in both electrostatic and magnetic environments.
It is a further object of the present invention to provide a method of manipulating charged particle beamlets and a method of focussing charged particle beamlets which are suited to provide particle-optical aberration correction.
Furthermore, it is an object of the present invention to provide an improved method of operating a particle-optical system and a method of manufacturing a multi-aperture plate suitable for use in the particle-optical component according to the present invention.
It is a still further object of the present invention to provide particle-optical components that allow adjusting a numerical aperture of charged particle beamlets. It is another object of the present invention to provide a particle-optical component that enables testing of a position or other properties of a multi aperture plate and/or optical properties of other optical components of a particle-optical system.